1. Field of the Invention
This invention relates in general to magnetic heads which are used to read and/or write magnetic data onto a magnetic film, and more particularly to heads using magnetoresistive materials and methods for making these heads.
2. Description of Related Art
Progress in magnetic data recording requires higher densities which in turn require increased sensitivity of the transducers (heads) used to read and write the magnetic signals. Noise reduction and protection of the heads from transient events and are important goals for the design of the heads. Many read heads operate using magnetoresistive materials, hence are called MR heads. The elements of a basic prior art MR read head with two shields are illustrated in FIG. 1 which shows a cut away view of the layers found in one type of prior head for use in a disk drive. As is typical this head has separate structures for the read and write functions. The portion performing the write operation of the overall head is often called the write element or the write head. The write element in FIG. 1 is an inductive head. The reading function is performed by elements which are called the MR head. A permeable magnetic layer 111 which acts as a first shield (S1) is deposited on an insulating layer 101 which is supported by a substrate layer (not shown). A first insulation layer 103 follows. The magnetoresistive (MR) element 114 and its leads (not shown) are deposited onto the insulation layer 103. A second insulation layer 104 follows in effect sandwiching the MR element 114 between the two insulating layers. On top of the second insulating layer, a permeable magnetic material is deposited forming a second shield (S2) 222. The elements which function together as an inductive write head include additional insulating material 107 and the induction coil 112 which is deposited in insulating layer 110. Layer 109 acts a pole piece for the write head. The S2 layer 222 serves a dual role by acting as the other pole piece in this particular type of head, but other designs including tape heads use separate layers for these functions.
The head of FIG. 1 is intended for use in a disk drive, but the basic elements and functions are the same for heads intended for tape drives. Tape heads are generally constructed with the read and write elements arranged side-by-side and S2 does not serve a dual role as a pole piece.
FIG. 2 illustrates a simplified cutaway view of the read elements in another type of prior art MR head called a ferrite head. Layer 61 is composed of ferrite with layer 61 acting as the S1 shield and layer 65 is a magnetic or nonmagnetic closure element. Shield S2222 and the MR element 114 are surrounded by insulating material 67. The MR lead 63 (which can be a conductive material such as gold) is shown connecting to the bias supply 17. MR heads such as the type illustrated in FIG. 2 have only one metal shield. The magnetic media travels past the gap formed by the two shields which act to block the magnetic field from the media outside of the gap. A constant dc bias current is applied to the MR element and the fluctuation in the voltage level across the MR element caused by the fluctuation of the resistance is the output signal.
FIG. 3 illustrates a simplified cutaway view of another type of prior art MR head. In this head the S1 shield is a separate element 111 as is the S2 shield 222. The two shields do not need to be made from the same material. The two shields and the MR element 114 are surrounded by insulating material 67 which is deposited in several steps during the manufacturing process. The MR lead 63 is connected to the bias supply 17 as before.
There are many variations of MR head design which can be seen in prior art references such as U.S. Pat. No. 5,713,122. MR heads are currently used in disk drive systems and tape drives. Although heads in disk drives are packaged with a single read/write element pair in a unit, a tape head assembly will have a read/write element pair provided for each track in a multitrack system.
A particular noise phenomenon has been observed in data readback from magnetic tape with MR heads. In the following "MR heads" will be used to include heads using the giant magnetoresistive (GMR) effect as well the magnetoresistive effect. The output signal from the read head has been observed to contain very sharp spikes which approximate ideal pulses with very narrow width and broad spectral content. These spikes can be of either polarity and are distributed over a range of amplitudes. The output signal from a head is typically passed to a preamplifier then into an input channel which includes various filters, detectors, decoders, error correctors, etc.
The effect of the sharp spikes in the input channel signal is at least randomly dispersed, correctable single bit errors and at worst may interfere with detection of the media signal. The spikes can occur in the absence a recording signal or MR bias current, but appear to require media/head contact and relative motion.
There are schemes designed for esd protection of the elements, but these do not directly relate to the present problem. There have been proposals for and tests of heads with various schemes, such as connecting the MR shields to ground in disk heads via resistors. However, connecting the shields to ground via resistors might actually aggravate the spiking problem by building in a constant large MR-shield potential difference as the discussion below will show.